The present invention relates to cardiac catheters and, more particularly, to an ultrasonically marked cardiac catheter for use in conjunction with an echocardiograph image display system.
Cardiac catheterization requires the accurate positioning of a catheter within the heart. Since the catheter is not visible, positioning thereof is commonly accomplished through the use of an X-ray system which displays an image depicting the position of the catheter within the body.
However, the use of an X-ray imaging system has various disadvantages. The ionizing radiation is a hazard to the patient and the medical staff. It requires the injection of large volumes of toxic iodine contrast to provide the necessary image clarity. The iodine contrast disturbs the patient's basal haemodynamics and may have toxic effects. It provides only a relatively poor spatial anatomy of the heart. In addition, the equipment required is expensive and requires extensive installation and a large amount of space.
Two-dimensional echocardiography, on the other hand, provides superior spatial anatomy of the heart, involves no irradiation hazard, and requires only small volumes of non-toxic echo-contrast material which does not adversely effect the patient's basal haemodynamics. In addition, the cost of echocardiography equipment is significantly lower than X-ray equipment.
For definitive cardiac diagnosis by ultrasound, intracardiac pressure recording and blood sampling are required for the calculation of intracardiac shunts, in many instances. In order to perform these operations, accurate positioning of the catheter is necessary. When echocardiography is employed, it is necessary that the portions of the catheter in the cardiac cavity be properly marked. Otherwise, accurate catheter positioning is not possible because an unmarked catheter entering or leaving points when intersecting the scanning plane of the echocardiograph can often be misinterpreted as the cathether tip. It is therefore necessary, if an ultrasonic imaging system is to be used for cardiac catheterization, that the catheter be marked in a way that provides an accurate method of determining the position thereof relative to the tissue.
For other types of medical procedures utilizing ultrasound techniques, such as aspiration biopsy, a hollow rigid metal needle has been used through which a point source omnidirectional transducer is inserted. The transducer is electrically connected to the imaging system by wires which extend through the lumen in the needle. Once the needle is properly positioned, the transducer is withdrawn by pulling the wires and, hence, the transducer, back through the needle. After the transducer is withdrawn, the biopsy procedure can take place. This method is, however, not suitable for use in a cardiac catheter because of the rigid metal needle and because the transducer position is not fixed relative to the needle tip and may move relative thereto as the needle is inserted.
It has also been suggested that transducers of various types be permanently mounted within the lumen near the tip or at the base of the needle. However, in such instances, the transducer is necessarily uni-directional, making the apparatus unsuitable for use as a cardiac catheter, even if the needle could be made flexible. Further, a transducer mounted within the needle lumen and the wires connected thereto obstruct fluid flow through the lumen and, therefore, may require separate passageways, resulting in a bulky, difficult to manipulate device.
In general, the present invention overcomes the above problems by providing a cardiac catheter which is flexible and easily manipulatable and which permits accurate omnidirectional positioning through the use of one or more tubular ultrasonic transducers mounted in spaced relation in the wall thereof. Since the transducers and the wire leads therefrom are embedded within the catheter wall, the lumen is unobstructed and the proper electrical isolation is achieved. Because the transducer is embedded in the catheter wall, it is in a fixed position relative to the catheter tip and, thus, accurate positioning of the tip is possible. Because the transducer does not obstruct the lumen, it need not be withdrawn prior to the performance of the medical procedure.
It is, therefore, a prime object of the present invention to provide an ultrasonically marked cardiac catheter.
It is another object of the present invention to provide an ultrasonically marked cardiac catheter which does not require the withdrawal of the ultrasonic marking means prior to the performance of medical procedures.
It is another object of the present invention to provide an ultrasonically marked cardiac catheter wherein one or more ultrasonic transducers are embedded within the catheter wall.
It is another object of the present invention to provide an ultrasonically marked cardiac catheter for use in conjunction with an ultrasonic imaging and display system to permit accurate omni-directional positioning of the catheter tip.